Laminated safety glass is widely used in motor vehicle windscreens, as bullet-proof glass, for example for protecting bank and post office counters, and as window glass, for example for reducing the danger of injury in the event of breakage and also, for example, as a safeguard against burglary and theft.
The interlayers used in these laminated glasses have to satisfy numerous, very stringent requirements. The following properties, in particular, are of considerable importance, especially for the use of laminated glass in motor vehicles:
1. A high energy-absorbing capacity in the event of sudden stressing as encountered on impact with blunt, but also sharp-edged bodies. PA1 2. Adequate glass adhesion which is intended to prevent the glass from shattering to any significant extent and causing injuries in the form of cuts in the event of accidents. PA1 3. High translucency; no hazing or clouding should occur. PA1 4. A high degree of light stability, in other words the windscreens should not turn yellow, even after prolonged exposure to sunlight. PA1 5. High edge stability so that, when stored before fitting, the windscreens should not undergo any delamination from the edges through the absorption of water. PA1 (a) a content of urea groups --NH--CO--NH-- amounting to between about 1 and 20% by weight and PA1 (b) a content of lateral carboxyl groups --COOH directly attached to the main chain of the molecule amounting to between about 0.001 and 10% by weight. PA1 (a) the dihydroxy carboxylic acid used corresponds to the formula ##STR1## in which R represents hydrogen or an alkyl radical with 1 to 4 carbon atoms, the quantity in which this dihydroxy carboxylic acid is used being such that the polyurethane polyurea obtained contains from 0.001 to 10% by weight of lateral carboxyl groups, and PA1 (b) the quantitative ratios between diisocyanates, dihydroxyl compounds and diamines are selected so that the polyurethane polyurea contains from 1 to 20% by weight of urea groups --NH--CO--NH--. PA1 (a) the relatively high molecular weight diols known per se from polyurethane chemistry having molecular weights in the range from about 300 to 6,000, preferably from about 800 to 3,000, PA1 (b) dihydroxy carboxylic acids corresponding to the formula ##STR2## in which R represents hydrogen or an alkyl radical with 1 to 4 carbon atoms and, optionally, PA1 (c) low molecular weight aliphatic or cycloaliphatic diols preferably having molecular weights in the range from about 62 to 300. PA1 1. Glass-clear, highly transparent polyurethane polyurea films are produced by a process which is simple and economic in practice having the particular advantage over conventional films that they adhere strongly, for example to glass, and are therefore particularly suitable for the production of laminated safety glass. PA1 2. Composite glass panels containing the interlayer films according to the invention are particularly superior in regard to their behavior under impact both at elevated temperatures and at low temperatures such as are frequently encountered in panels exposed to weathering.
These properties in general and those mentioned under (1) and (2) in particular should be retained over as wide as possible a temperature range in which these materials are used.
In modified form, these requirements also apply to the use of the interlayers in armoured glass and in safety glass of the type used in building construction. Armoured glass is above all required to be bullet proof to a large extent. This makes it necessary to use an extremely tough interlayer.
Polyurethane interlayers for laminated safety glass are already known. Thus, according to German Offenlegungsschrift No. 2,302,400 (corresponding to U.S. Pat. Nos. 3,823,060 and 3,900,446), polyurethane interlayers for laminated safety glass are produced from 4,4'-methylene-bis-(cyclohexylisocyanate), a polyester containing terminal hydroxyl groups and having a melting point above 42.degree. C. and a molecular weight of from 500 to 4,000, being the condensation product of a dicarboxylic acid and a diol compound, and a chain extender which is an aliphatic or alicyclic diol containing from 2 to 16 carbon atoms.
Unfortunately, conventional polyurethanes have the serious disadvantage of poor adhesion to glass. However, glass-plastics laminates are intended to be of a structure such that no splinters of glass can be released from the plastics interlayer of the laminated glass in the event of a collision. This requirement is not satisfied by conventional polyurethanes (cf. Example 7).
Accordingly, the object of the present invention is to obviate the above-mentioned serious disadvantage of conventional polyurethanes and, in addition, to provide polyurethane polyaddition products of the type which, in addition to excellent adhesion to glass, show outstanding impact strength over a wide temperature range, are free from hazing and local swellings, do not discolor on exposure to sunlight and show excellent edge stability with respect to penetrating water.
This object is achieved by the polyurethane polyureas provided by the invention.